Both acute and chronic bioassays are performed using Ceriodaphnia dubia and Pimephales promelas (fathead minnows) to determine the toxicity of the water.

Ceriodaphnia dubia

Ceriodaphnia dubia are freshwater organisms used in both acute and chronic toxicity testing. They are most commonly known as water fleas and inhabit lakes, ponds and marshes throughout much of the world. Neonates utilized in acute toxicity tests are introduced into five dilutions of the sample for 48 hours. Mortality and simple water chemistry are monitored at test start, after 24 hours, and at test end. At test completion, a statistical program (CETIS) is used to generate a LC50/TUa (the concentration at which 50% of the organisms are affected).

In chronic toxicity testing, Ceriodaphnia neonates are monitored for 7 days or until 60% of the control organisms have three broods of offspring. During the test, organisms are placed into fresh sample dilutions daily and mortality and offspring are monitored and recorded. At test completion, a statistical program is used to generate the LOEC (lowest observable effected concentration), NOEC (no observable effected concentration) and IC25.

Pimephales promelas

Pimephales promelas commonly known as fathead minnows are cultured in house and are maintained in a recirculating system. P. promelas used for acute testing may be 1-14 days of age and are introduced into 5 sample dilutions for 48 hours. As with Ceriodaphnia, P. promelas undergo the same monitoring and statistical evaluation.

Pimephales promelas used in chronic testing must be <1 day old. Test chambers are cleaned and new sample media is introduced daily. Mortality is monitored for 7 days and at test end, the organisms are dried to determine if organism growth was affected. CETIS, a statistical program, is used to generate the LOEC, NOEC and IC25.